System and method of determining distance



Jan. 524, 1939. R. B. HEARN 2,

SYSTEM AND METHOD OF DETERMIN ING DISTANCE Filed April 7,1936

FIG. 2

uwmrok 2 By RBI-{EARN fai -8W ATTORNEY/ Patented Jan. 24, .1939

PATENT OFFICE SYSTEM AND METHOD OF DETERMINING v DISTANCE Richard B.Hearn, Hollis, N. Y., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y.,' a corporation of New York ApplicationApril 7, 1936, Serial No. 73,116

- I 4 Claims. This invention relates to the determination of distancesby means of longitudinal waves and has for an object to measuredistances, particularly relatively short distances, accurately andprecisely.

One of the hazards of aeronautics that has commanded consideration'inrecent years is the difliculty incident to the landing of airplanes whenatmospheric visibility is poor.

It has long been known that distances may be ascertained by theproduction of sound waves, and the determination of the period requiredfor these waves to tnavel to and return from a reflecting surface. tweenthe emission of the waves and their reception after reflection isdirectly correlated with the distance between the source and thereflecting surface, long distances may be easily estimated. However,short distances arediflicult to ascertain, due to the short intervalbetween the emission of the waves and their reception after reflection.

, suitable receiving device.. This invention pro-,

In accordance with this invention, longitudinal vibrations which producewaves such as audible or superaudible waves are employed to measurerelatively short distances, such as the height of an airplane above theearths surface. For example, an .airplane may be provided with a sourceof sound waves, which waves are reflected by the earths surface back-tothe airplane to a vides means for producing a current or voltage,

' the magnitude of which is proportional to the charging a condenserthrough a high resistance at the instant the wave train is transmittedand to stop the charging of the condenser the instant the wave isreceived after reflection from. the earth's surface, so that themagnitude of the charge on the condenser is proportional to thealtitudeof-the airplane. The charge on the ondenser is then measured, forexample, by discharging the condenser through the primar, winding of atransformer having a second condenser and a rectifier connected inseries with its output winding. The voltage on this second condenser maybe used to control the grid voltage of a vacuum tube amplifier having adirect current measuring instrument in its output circuit. It willbe'apparent thatthe reading of the I Fig 2 is a modification of Fig. 1.

Since'the time which elapses be-'- meterwill be proportional to thealtitude "of the;

airplane above the ground.

- Referring tothe drawing:

Fig. 1 represents a schematicaltitude indicator for airplanes; and. 8

The apparatus -of Fig. 1 is adapted to' be mounted in an airplane toenable its altitude to be readily determined. The numeral 3 representsan instrumentality such as a moving coil I'd type loud-speaker with aneirponential horn which serves to transmit and receive longitudinalwaves, such as sound waves, employed in the determination of the heightof the airplane above the earth 4.. It will be apparent that when a 15sound of short duration is emitted by loudspeaker 3, the sound waveafter. striking the earth or other bounding surface will be reflectedand part of the reflected wave will be received by loud-speaker 3 sothat the time which elapses .0 between the emission of the sound wave byloudspeaker 3 and its reception after reflection is proportional to thealtitude of the airplane above ground. This invention, as exemplifiedinFig. 1, provides means for producing a voltage the magnitude of which isproportional to this elapsed time and the deflection of the meter formeasuring this voltage will be a direct indication of the altitude'ofthe airplane.

The source of. audible or superaudible frequency oscillations employedin the altitude measurement may comprise a conventional reverse feedbackoscillator 6 comprising a space discharge device 5 connected toloud-speaker 3 by means of a transformer I through the hybrid 5 coil 8.This type of oscillator'is illustrated, for example, in Fig. 11 of anarticle entitled Constant frequency oscillators -by F. B. Llewellynpublished in the Proceedings of the Institute of Radio Engineers forDecember 1931, vol. l9, 40

pages 2063'to 2094. .The voltage drop across a resistance 9 in the inputof space discharge device 5, causedby the flow of current through theserially connected resistances 9 and I0 ordi- .4

. to oscillate is secured in Fig. l by permitting the charge on-acondenser I! to discharge through resistance 9-in sucha .manner as toneutralize in part, at least, the-IR drop in resistance 9-.due

to battery i3.

- For the purpose of describing the operationof the arrangement of Fig.1, it may beassumed. 6c

A that oscillator 6 has been made operative for a short interval of timeto cause loud-speaker 3 to emit a train of sound waves which, afterreflection from the earth's surface is again received by loud-speaker 2and impressed through a band-pass filter it upon a suitable amplifierll. Amplifier I5 is coupled to the input of a vacuum tube It, the outputcircuit of which may be traced from anode I1, conductor ing polarrelay8, upper winding battery and ground, back to the I. The reflected waveafteramplification by amplifier I5 is sufilcient to cause appreciablespace current to fiow in tube It and thereby cause polar relays S and Mtomove their armatures against their left contacts as shown in Fig. 1.The movement of the armature of polar relay S against its left contact22 establishes a circuit from positive battery, winding of relay P, leftcontact 22 of relay S, resistance "and condenser l2 to ground so thatthe closure of this circuit by p'olar relay M, filament of tube relay 8serves to charge condenser i2. through the winding of relay P. Thischarging current serves to operate relay P.to close its contacts andenergize relay R by closing a circuit from battery, contact of relay T,winding of relay R and contact of relay P to ground. Relay R in closingits right contact serves to connect ground to conductor I! to establisha temporary holding circuit for relays M and S after the amplifiedreflected impulse has ceased. Relay R in closing its left contactestablishes a circuit from battery, 00nr t e erated.

i9, upper wind-.

it will be apparent that relay s again'causes relay. R, and T'to operatein the manner preview, described t permit condenser I2 to subseq e tldis harge through resistance 9 of the antor to cause another short trainof audio frequm oscillations to be gen- F'I'Om the above desclnmon It]:apparent each time the armature gill-clay s is moved to 01086 its rightcontact 2|, train of sound waves is emitted by loud-speaker and the said1 time remains on contact 2| r t t sound wave after reflection from theearth' surgacehas ere'd the impedance of'the space current path of tubeIt to cause the armature o polar relay 3 to move against its leftcontact 21. The l th of time that armature 24 remains against contact 2|is, therefore, proportional to the altitude of loud-speaker 3 above thereflecting Surface 4.

Polar relay M is similar to polar relay 3, and a M will operate in thesame manner as relay S and simultaneously therewith. When relay 8 closesits right contact 2| to render oscillator 8 operative, relay M closesits right contact to close a charging circuit for a a condenser 28',which circuit may be traced from battery, high resistance 21, rightcontact relay M and condenser 26 to ground. As soon as the reflectedsound wave has caused relay 8 to close its left contact 22, relay M alsoopens its right 30 contact and closes its left contact. The VOIWECobserved that relays R and T could be eliminated and the contact ofrelay P connected directly to conductor l9 providing relay P could bemade very fast to operate and slow to release. Since such a combinationis difficult to obtain in one relay, relay P is made fast operate andthe slow release feature is obtained by adding relays R and T as shownin the drawing. It will be apparent that. the general object of relaysP, R and T is to permit condenser 12 to receive a full charge throughrelay P before ground 44 has been removed from conductor l9. Relay P mayrelease before condenser I2 is fully charged but the charging willcontinue while relay T operates and relay R releases.

It will be apparent from Fig. 1 that balancing network N is connected tohybrid coil 8 in the usual manner to prevent any of the output currentfrom oscillator 6 from being received directly by receiving amplifier ISwithout first having be of any. suitable type, such as a direct currentmicroammeter.

It will be understood that the duration of each train of waves fromsource 6 should be short compared to the time required for the soundwaves to travel from loud-speaker 3 to the earth and back toloud-speaker 3.

The embodiments of the invention described above are for illustrativepurposes since the invention is capable of other forms commensurate withthe scope of the invention as defined inthe appended claims.

What is claimed is:

1. An altimeter comprising an oscillator arranged to generate audiofrequency waves but normally inoperative, adevice for translating saidwaves into sound waves, means for rendering said oscillator operativefor a predetermined relatively short interval of time, a receivingdevice responsive to said sound waves after reflection from the earthssurface for wholly controlling said means, a condenser, means controlledby the receiving device for charging said condenser to a potentialsubstantially proportional to the .instrument for measuring thepotential of said condenser.

2. In a time measuring system, a first means for producing anddirectiv'ely emitting a sound pulse comprising a tube oscillatorincluding a cathode and a control electrode, the pulse duration beingshort relative tothe time interval included between the emission of thepulse and its return from a given reflecting surface, a second meanscontrolled only by the pulse received after reflection from said surfacefor rendering said control electrode negative with respect to thecathode after emission and continuously during propagation of the pulseand positive shortly after reception of the pulse, a condenser, and athird means controlled by the second means for charging said condensercontinuously during said time interval and only during said interval,and indicating. means for measuring the charge of said condenser.

3. A system for measuring time or distance comprising a normallyinoperative audio frequency tube oscillator having an input circuit andan output circuit, a device connected to the output circuit fortransmitting a pulse produced bysaid oscillator and receiving said pulseafter reflection from a surface, a condenser, means connected to thedevice and actuated by the re-' ceived pulse for charging the condenserand upon charge of said condenser for simultaneously discharging thecondenser and applying the decreasing condenser voltage to' 'theterminals of the input circuit whereby the oscillator is renderedoperative during only the discharge period of the condenser anda shortpulse of predetermined duration is emitted by the'device, and meanscontrolled by the received pulse for measuring and indicating the timeinterval included between the emission and return ofthe pulse.

4. In a system for measuringtime or distance. a tube oscillator havingan input circuitand an output circuit, a device connected to the outputcircuit for transmitting waves produced by said oscillator and.receiving said waves after reflection from a given surface, a firstcondenser, a second condenser, a relay, a voltage means connected inseries with said relay and the flrst condenser, a voltage measuringmeans including a discharge path connected in circuit with the secandcondenser, a switching means controlled by and actuated upondeenergization of said relay for [disconnecting the first condenser andthe voltage means and the second condenser and the measuring means andsimultaneously therewith for connecting the second condenser in serieswith the voltage means andthe flrst condenser in shunt with a portion ortheoscillator input circuit whereby said first condenser discharges andsaid oscillator is rendered operative during only the discharge periodof the first condenser, and a second means connected to said device andachiated by the energy received thereby for restoring the switchingmeans to normal.

